Balancing propeller blades



g 1947' G. T. LAMPTON ET AL ,4

BALANCING PROPELLER BLADES Filed Nov. 5, 1942 Patented Aug. 26, 1947BALANQING PROPELLER BLADES (lien T. Lampton, Hartford, Conn, and Don R.

Woolf, Toledo, Ohio, assignors to Avco Manufactoring Corporation, acorporation of Delaware Application November 5, 1942, Serial No. 5164,674

9 Claims. (Cl. 1707-159.)

The invention relates generally to propellers for aircraft, and moreparticularly to a method of, and devices for, statically balancing theblades about their longitudinal axes.

In practice the moments of the weights of the blades of a propellerabout its axis of rotation should be equal in order to minimizeunbalance and prevent vibration stresses which may exceed the designatedlimits and cause failure in affected parts of theengine-propeller-airplane combination. It is likewise necessary thateach propeller blade be balanced around its longitudinal axis for thesame reasons. It is possible to balancea propeller blade about its axisof rotation and at the 'same time have the propeller blade unbalancedabout its longitudinal In the manufacture of propeller blades it hasbeen found relatively easy to correct one .or the other of theseimbalances individually, but difficult to correct or maintain bothbalances. It is now common procedure in correcting unbalance to add anamount of metal or mass, usually solder, lead or type metal, in thecavity of the shanl; of the propeller blade proportional tothe-unbalance of the propeller blade. If the blades of a propeller arebalanced about its axis of rotation and any blade is unbalanced aboutits longitudinal axis, metal added to correct the unbalance about itslongitudinal axismay destroy the balance moment about the axis ofrotation of the propeller. The

present invention contemplates the fabrication of blad s y the additiono the s me or a predetermined Wei ht of meta toall bla s-and variae 1 1of s di s t on are dits longitu in axis for balance moment around thelongitudinal a is a a n m i ta e from t e ax s of rotation of thepropeller so as to maintain the balance between h b d s a p op lle Th efect of the weight is varied by a change of its position around thelongitudinal axis of the blade without increase or decrease of theweight, for correction f any unbalance ab ut the longitud a T d i f i hQ e ua am unt to each blade for said purpose Wil not change the balanceof the blade around the axis of rotation of the propeller o thatrelatively the balance remains unchanged.

One object of the invention is to provid a method of correcting anunbalance ondition in a propeller blade about its longitudinal axiswithout affecting the balance of the bladesabout the axis of rotation of thepropeller. 7

Another object of the invention isto. provide a method of staticallybalancing propeller bl d a u t e long tud nal a ebr a d n mas correctpositions to rectify the unbalance according to the magnitude and radialdirection of the unbalance caused by variation inthe physical dimensionsof the blades so that the blades after being balanced around theirlongitudinal axes are of uniform balance and will ibe staticallybalanced relativeto each other.

' Another object of theinvention is to provide a mass of predeterminedweight With component parts which are adapted respectively to be fixedlyplaced-in any radial direction in the shank of a propeller blade so thatthe resultant moment of the mass will be equal in magnitude and inopposite direction to the unbalance moment of the blade.

Another object of the invention is to provide eccentric weights of equalbalancing moment which by positioning relatively to each other can bemade to correct any unbalance from an unbalance equal to the sum of thebalancing moments of the eccentric weights to no unbalance inclusive.

Another object of the invention is to provide a mass for adding weightsfor balance around the longitudinal axis of'the blade, which is composedof eccentric weights of difierent radii'and equal balancing momentswhichcan be rotatively positioned to all radial positions before beingpermanently fixed in the blade.

Another object of the invention is to provide a standard set of weightsfor compensating for the unbalance about the longitudinal axis of theblade producedby loads of difierent magnitudes and located in any radialdirection.

Other objects of the invention will the detailed description.

The invention consists in the several novel features which arehereinafter set forth and are more particularly definedby claims at theconclusion hereof.

In the drawings: Fig. 1 is an elevation, a propeller bladeembodying theinvention.

Fig. ;2 is a longitudinal section of the shankappear from portion of theblade and the balancing weights on an enlarged scale.

Fig. 3 is a perspective of one of the balancing sections which comprisesa ring and a weight.

Fig. l is .a perspective of the other balancing section with the weightthereon.

Fig. 5 is a section taken on line 15+-5 of Fig. 2. Figs. .6, 7,8, ,9 and1( are similar sections, respectively, showingthe balancing weights indiferen ion iii h ade- 'E 1.1 i a i fi l'i i f th a allelo ram 9?partially in section, of

forces through the use of which the effective magnitude and position ofthe load which causes the unbalance may be determined.

Fig. 12 is a diagrammatic View illustrating a propeller indicating thelocation of the balancing weights relatively to its axis of rotation andthe longitudinal axis of the blade.

- The invention is exemplified in connection with a steel propellerblade 11 having a hollow shank a The shank of the blade may be securedin a propeller hub in any well known manner. The blade is completelyfabricated before the mass for statically balancing it about itslongitudinal axis is added. The shank a is counter-bored as at a to anannular shoulder a to receive the balancing mass. The longitudinal axisof the blade is indicated by the line ZZ in *Fig. 1. A plurality ofblades are usually secured in a hub and are rotatable together on theaxis indicated at !5.R,

in Fig. 12. In practice the blades are usually finished to apredetermined balance moment about the axis of rotation R-R before theyare statically balanced about their longitudinal axes ZZ.

The invention provides for the addition of a standard mass for allproduction blades of a similar character and which mass is composed ofsections for statically balancing the blade about its longitudinal axisto compensate for any unbalance. Due to production methods the unbalancein different blades will probably be of differing magnitudes and requiredifferent positioning of the standard mass. Generally the imbalance isproduced by inaccuracies in physical dimensions and may be located inany radial direction from the axis. These sections comprise twoeccentric weights of equal balancing moment about the axis ZZ and whichcan be separately positioned in any radial direction relatively totheaxis ZZ of each blade. By adding'to each blade, the standard mass oreccentric Weights at an equal distance from the axis RR, for staticbaiance about axis ZZ, the moment of all blades about the axis R-R willbe the same. If there is no unbalance about the longitudinal axis Z- -Z,the weights are located in mutually balancing radial positions in theblade but the blade Will have the same moment about the axis R-R as theblades wherein it was necessary to balance about. the axis ZZ. Thesections of the mass hereinafter described are adapted to add to eachblade, mass of uniform weight. V

For brevity, the balance about the longitudinal axis ZZ of the blade ishereinafter referred to as the vertical balance and the balance of theblades about the axis of rotation RR is referred to as the horizontalbalance.

The mass for vertical balance of the blade comprises a pair of separatesections and b, each of which has an integral weight. The weights are onthe sections, respectively, and. adapted to be circumferentiallypositioned in the counterbore a of the shank in any radial directionthrough 360. Section b comprises a ring M of metal which has an end-facel5 which is adapted to abut against the annular shoulder a in the shanka to position it longitudinally in the shank and a cylindrical peripheryH5 which is adapted'to fit into the bore a so that the ring will fit andis rotatable concentrically to any position in the shank. Section 7) hasan eccentrically located weight b which is integral with ring; hi andadapted to be rotatively positioned at a uniform distance around theaxis ZZ,- projectslongitudinally inward from the ring 14, and has anouter arcuate face concentric with the longitudinal axis 4 of the bladeand a chordal inner face. The section 0 comprises a wall ll which has acircular periphery concentric with axis ZZ and fitting in ring l4.Section 0 is formed with an annular flange [8 which fits in acounterbore is in the outer face of ring M, and with an integral weight0 Said weight 0 is eccentrically located, is rotatable around axis ZZ toany radial direction with section 0, projects longitudinall inward fromring ll, and has an arcuate outer face concentric with the said axis,and has a, chordal in ner face. These weights are located on. differentradii so they are rotatable past each other and so that each can be setinto any radial direction around the axis of the blade," before beingfixed therein, and are preferably of the same length. The balancingeffect of each weight about the longitudinal axis of the blade is aproduct of its mass, times the distance of the center of mass from thelongitudinal axis of the blade. The mass of the inner weight 0 on theshorter radius is greater than the mass of outer weight b on the greaterradius, and they are proportioned to produce equal balancing momentabout the longitudinal axis of the blade. Ring 14 and crosswall I! areeach provided with sockets e for receiving a turning tool or wrench forrotating them in the shank into the radial directions desired. Thisconstruction adapts the sections for rotative positioning of the weightsin the shank and relatively to each other into any radial direction toeffect static balance of the blade around its longitudinal axis and forpermanent attachment to the blade thereafter.

In carrying out the invention, the magnitude of unbalance and thelocation of the load which produces it, for calculation of the radialdirections in which the eccentric weights must be placed to compensatefor the unbalance, are first determined. For this purpose, the blade issuccessively supported for movement across radial planes perpendicularto each other and the unbalance in each plane is measured. Any suitabletesting apparatus may be used for this purpose. The unbalance is usuallymeasured in units of an ounce inch which is the unbalance due to aweight of one ounce locatedaradial distance of one inch from the axis ofthe blade. The two rectangular components of the force which producesthe unbalance by the tests in axial planes which are perpendicular toeach other, are measured. The location of the force and its magnitudewhich produce the unbalance are determined by laying out vectors fromthese components. For example, in Fig. 11, assuming the load whichcauses the unbalance to be located at W the load across the plane X+X iswx and the load which causes the unbalance across the plane Y-Y to bemy, then the unbalance of the load would be equivalent to a weight W inthe angular direction -0 and at a distance 'r from the axis Z-Z. Theangular direction 0 and the magnitude of the load W can then becalculated from the parallelogram. From. these resultants the radialdirections in which the eccentric weights of predetermined moment mustbe placed oppositely to said load in orde to add mass to accuratelycompensate for the unbalance produced by said load, are calculated. Theblade is indexed or marked for the planes in which the measurements aretaken. The compensating angles or radial directions for the weights areindexed on the ring b and section 0. The ring I) and section 0 are thenplaced in the bore a with the ring seated on the shoulder a and thesection 0 seated on the ring 12 so that'the'centers of mass oftheweights b 'c will be positioned in the indexed radial directions inwhich they will compensate for the measured unbalance caused by the loadW according to its position in the blade and its magnitude.

The construction of the ring I) and section a adapts each of theeccentric weights to be positioned in any radial direction from the axisZ-Z of each blade so that measured loads of differing magnitude and inany portion of the blade may be accurately compensated for. The bladewith the weights set in compensating radial directions may then be againtested in perpendicular planes to determine whether the Weights havebeen set for accurate static balance around the longitudinal axis of theblade. If the unbalance "is accurately compensated for, the sections 1)and c are permanently secured in the shank a} by brazing'or soldering.Figs. 6, 7, 8, 9 and 10 illustrate some of the different radialpositions in which the weights are adapted to be fixed for compensationfor the unbalance of different magnitudes caused by loads in differentportions of the blade. If the weights as shown by the second testindicate any slight error. in calculation, they can be rotated untilthey are radially directed for accurate balance before they are fixed inthe blade. if the initial tests in planes perpendicular to each otherindicate no unbalance, the weights are located in diametrically oppositepositions, as illustrated in Fig. 5 or 8, where they will add mass tocorrespond to that added to other blades for balance around axis R-R. Inthus statically balancing the blades, a plurality of sections of massesof uniform weight are added to each blade and the weights are rotatedinto positions to compensate for the unbalance. Each pair of sectionsprovides a standardized Weight-constructionfor all blades.

In carrying out the foregoing method the total weight added-to each ofthe blades fo vertical balance and the distance each weight is locatedfrom the axis of rotation RR is identical in all blades. The change ofthe longitudinal center of gravity caused by the addition of the Weightsfor vertical balance is the same in all blades so that they will havethe same moment of force to avoid disturbance of the static balance ofthe blades in the propeller. As a result, the vertical balancing of theblade is attained without disturbing the horizontal balance.

A screw-stud 23 is threaded through the crosswall I! of section 0 forlongitudinally balancing the blade within precision limits to compensatefor production limits or tolerances of the sections b and 'c. Thesections b and c with the stud 23 therein, When secured in the shank ofthe blade, form a closure or plug for sealing the chamber in the workingportion of the blade which prevents the admission of oil to said chamberfrom the hub in which the blade is mounted, and also excludes moistureand prevents resultant corrosion.

The invention exemplifies a method for producing vertical balance of apropeller blade which comprises adding to and fixing in the shank of allblades of one type a uniform mass composed of a plurality of sectionsprovided with eccentric weights and positioning the weights in differentradial directions to compensate for the unbalance of the particularblade in which the weights are positioned and maintaining the horizontalbalance of all of the blades substantially the 6 same. The same totalweight is added to all blades and at the same distance from R ft.

The invention also exemplifies simple and enicient construction ofbalancing means which comprises a plurality of eccentric weights whichare adapted'to be placed and fixed in the blade in any radial directionto compensate for unbalance in any portion of the blade. The inventionalso provides a pair of sections with eccentric weights of standardconstruction for statically balancing blades about their longitudinalaxe for quantity production. The invention also provides a pair ofweight-carrying sections which function as a closure or seal whichexcludes oil and moisture in the chamber in the working portions of theblade.

The invention is not to be understood as restricted to the details setforth, since these may be modified within the scope of the appendedclaims without departing from the spirit and scope of the invention.

Having thus described the invention, what we claim as new and desire tosecure by Letters Patent, is:

1. A propeller blade, provided in its shank with a cylindrical herewhich is concentric with the axis of the shank, comprising a pluralityof elemerits, each provided with a mass of fixed weight having itscenter of gravity radially displaced irom the elements having means forconfining them for 'rotative positioning around the axis in the bore andrelatively to each other, with the radii and the weight of the massesremaining constant and whereby such positioning will compensate forunbalancing loads of difie'rent mag= nit-udes located in differentportions of the blade, theelenients being adapted to be fixedly securedin the bore of the blade, for balancing the blade about its"longitudinal axis, each mass extending and projecting at a difierentradius from the other and from the confining means and into the bore ofthe blade.

2. A propeller blade, provided in its shank "with a cylindrical borewhich is concentric with. the axisof the shank, comprising: an elementprovided with an annulus rotatively fitting in and adapted to bepermanently secured in the bore and with a mass of fixed weight havingits cen= ter ofgravi'ty one fixed radius from the axis; and a secondelement rotatably fitting and adapted to be permanently secured in saidring and provided with a mass'of fixed weight having its center ofgravity on a fixed radius from the axis said elements being'adapted tobe rotatively positioned in th bore, for compensating for unbalancedloads of different magnitudes located in difierent positions of theblade to balance the blade around its longitudinal axis and, whensecured in the bore, to balance the blade around its longitudinal axis.

3. A propeller blade, provided in its shank with a cylindrical borewhich is concentric with the axis of the shank, comprising: an elementprovidedfwith an annulus rotatively fitting in and adapted to bepermanently secured in the bore 7 and with a mass of fixed weight havingits center of gravity on a fixed radius from said axis; and a secondelement rotatably fitting and adapted to be permanently secured in saidring and provided with a mass of fixed weight having its center ofgravity on a fixed radius from said axis, said elements being adapted tobe rotatively positioned in the bore, for compensating for unbalancedloads of different magnitudes located in substantially all portions ofthe blade to balance the blade around its longitudinal axis and, whensecured in the bore, to balance the blade around its longitudinal axis.

provided with a fixed weight extending longitudinally from the ring andhaving its center of mass on a fixed radius from the axis; a secondelement having a part rotatively fitted in the ring and provided with afixed weight extending longitudinally from said part with its center ofmass on a fixed radius; said elements being adapted by rotativepositioning in the bore to compensate for unbalancing loads of differentmagnitude located in different positions of the blade and to bepermanently secured in the blade to balance it around its longitudinalaxis.

5. A propeller blade, provided in its shank with a cylindrical borewhich is concentric with the axis of the shank, comprising: an elementprovided with a ring confined in the bore and provided with a fixedweight extending longitudinally from the ring and having its center ofmass on a fixed radius from the axis, a second element having a partrotatively fitted in the ring and provided with a fixed weight extendinglongitudinally from said part with its center of mass on a fixed radius,said elements being adapted by rotative positioning to compensate forunbalancing loads of different magnitude located in substantially allportions of the blade and to be permanently secured in the blade tobalance it around its longitudinal axis.

6. A propeller blade, provided in its shank with a cylindrical borewhich is concentric with the axis of the shank, comprising: an elementprovided with a ring confined in the bore and provided with a fixedweight extending longitudinally from the ring and having its center ofmass on a fixed radius from the axis, a second element having a partrotatively fitted in the ring and provided with a fixed weight extendinglongitudinally from said part with its center of mass on a fixed radiusshorter than the radius of the weight on the ring, said elements beingadapted by rotative positioning to compensate for unbalancing loads ofdifferent magnitude located in different positions of the blade andadapted to be permanently secured in the blade to balance it around itslongitudinal axis.

7. A propeller blade, provided in its shankwith a cylindrical bore whichis concentric with the axis of the shank, comprising: an elementprovided with a ring having its periphery fixedly secured in the boreand a fixed weight extending longitudinally outwardly from the ring withits center of mass on a radius from the axis; and a second elementhaving a part fixedly secured in the ring and provided with a fixedweight extending longitudinally outward from said part, with its centerof mass on a radius from the axis, the said elements being adapted to berotatively positioned around the axis to points where the weights willcompensate for unbalancing loads of different magnitude located indifierent portions of the blade, before the elements are secured in theblade to balance it around it longitudinal axis.

8. A propeller blade, provided in its shank with a cylindrical borewhich is concentric with the axis of the shank, com-prising: an elementprovided with a ring having its periphery fixedly secured in the boreand a fixed weight extending longitudinally outwardly from the ring withits center of mass on a radius from the axis; and a second elementhaving a part fixedly secured in the ring and provided with a fixedweight extending longitudinally outward from said part, with its centerof mass on a radius from the axis, the said elements being adapted to berotatively positioned around the axis to points where the weights willcompensate for unbalancing loads of different magnitude located insubstantially all portions of the blade, before the elements are securedin the blade to balance it around its longitudinal axis.

9. A propeller blade, provided in its shank with a cylindrical borewhich is concentric with the axis of the shank, comprising: an elementprovided with a ring having its periphery fixedly secured in the boreand a fixed Weight extending longitudinally outwardly from the ring withits center of mass on a radius from the axis; and a second elementhaving a part fixedly secured in the ring and provided with a fixedweight eX- tending longitudinally outward from said part, with itscenter of mass on a shorter radius from the axis, the said elementsbeing adapted to be rotatively positioned around the axis to pointswhere the weights will compensate :for unbalancing loads of differentmagnitude located in different portions of the blade, before theelements are secured in the blade to balance it around its longitudinalaxis.

GLEN T. LAMPTON. DON R. WOOLF.

REFERENCES CITED ihe following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,903,817 Johnson Apr. 18, 19331,997,671 .Arnold Apr. 16, 1935 1,645,343 Moorhouse Oct. 11, 19271,590,840 Lundgren June 29, 1926 1,540,643 Lundgren June 2, 19251,876,527 Thearle Sept. 6, 1932 710,148 Hodgkinson Sept. 30, 19021,774,718 McCabe Sept. 2, 1930 1,191,393 Bergstrom July 18, 19302,364,131 Daniels et al. Dec. 5, 1944 FOREIGN PATENTS Number CountryDate 365,027 Great Britain Jan. 14, 1932

